1. Field of the Invention
Embodiments of the present invention generally relate to a method of tungsten film deposition and, more particularly, to a method of forming a tungsten film having good film morphology.
2. Description of the Related Art
In the manufacture of integrated circuits, tungsten (W) films are often used as contact metallization or plug metallization for interconnect schemes. Tungsten (W) films may also be used as a diffusion barrier for copper (Cu) in various metallization schemes.
The tungsten (W) films are typically composite films comprising a thin tungsten (W) nucleation layer (thickness of about 50 xc3x85 to about 150 xc3x85) and a thicker bulk tungsten layer (thickness of about 500 xc3x85 to about 2000 xc3x85) formed thereover. However, tungsten films comprised of a thin tungsten nucleation layer and a thick bulk tungsten layer tend to have poor film morphology. The morphology of a film refers to its surface roughness, and grain structure.
For example, tungsten (W) films comprising a thin tungsten nucleation layer and a thick bulk tungsten layer typically have large grain sizes (e.g., grain sizes of greater than about 10 nm/rms). Large grain sizes produce rough surfaces, which are undesirable for subsequent lithography steps performed thereover.
Therefore, a need exists in the art for a method of forming tungsten films having good film morphology.
A method of forming a composite tungsten film on a substrate is provided The composite tungsten film comprises sequentially deposited tungsten nucleation layers and tungsten bulk layers. Each of the tungsten nucleation layers and the tungsten bulk layers have a thickness less than about 300 xc3x85. The tungsten nucleation layers and the tungsten bulk layers are formed one over the other until a desired thickness for the composite tungsten film is achieved. The resulting composite tungsten film exhibits good film morphology.
The tungsten nucleation layers may be formed using a cyclical deposition process by alternately adsorbing a tungsten-containing precursor and a reducing gas on the substrate. The tungsten bulk layers may be formed using a chemical vapor deposition (CVD) process by thermally decomposing a tungsten-containing precursor.
The composite tungsten film is compatible with integrated circuit fabrication processes. In one integrated circuit fabrication process, the composite tungsten film may be used as word and/or bit line metallization to read and write data to memory cell devices. For a word and/or bit line fabrication process, a preferred process sequence includes providing a substrate having a word and/or bit line pattern defined in a dielectric material layer. The word and/or bit line pattern defined in the dielectric material includes a barrier layer thereon. Thereafter, a composite tungsten film comprising sequentially deposited tungsten nucleation layers and tungsten bulk layers, each having a thickness less than about 300 xc3x85, are formed one over the other on the barrier layer until a desired thickness for the composite tungsten film is achieved.